Semiconductor device and method of manufacturing same

ABSTRACT

A semiconductor device includes a substrate and a ferroelectric capacitor including a lower electrode, a ferroelectric film, and an upper electrode. The upper electrode includes a first layer formed of an oxide whose stoichiometric composition is expressed as AOx 1  and whose actual composition is expressed as AOx 2 ; a second layer formed on the first layer and formed of an oxide whose stoichiometric composition is expressed as BOy 1  and whose actual composition is expressed as BOy 2 ; and a metal layer formed on the second layer. The second layer is higher in ratio of oxidation than the first layer. The composition parameters x 1 , x 2 , y 1 , and y 2  satisfy y 2 /y 1 &gt;x 2 /x 1 , and the second layer includes an interface layer of the stoichiometric composition formed at an interface with the metal layer. The interface layer is higher in ratio of oxidation than the rest of the second layer.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application is a continuation application filed under 35U.S.C. 111 (a) claiming benefit under 35 U.S.C. 120 and 365 (c) of PCTInternational Application No. PCT/JP2007/055694, filed on Mar. 20, 2007,the entire contents of which are incorporated herein by reference.

FIELD

A certain aspect of the embodiments discussed herein is related tosemiconductor devices and methods of manufacturing same.

BACKGROUND

Ferroelectric memories, which are voltage-driven nonvolatilesemiconductor memory devices, have preferable characteristics such ashigh-speed operation, low power consumption, and nonvolatility ofretained information during power shutdown. Ferroelectric memories havealready been used in IC cards and portable electronic devices.

Ferroelectric random access memories (FeRAMs), which may be typicalexamples of ferroelectric memories, include a ferroelectric capacitorhaving a ferroelectric film held between a pair of electrodes, and storeinformation by inducing polarization in the ferroelectric capacitor inaccordance with the voltage applied between the electrodes. Theinformation thus written into the ferroelectric film in the form ofpolarization is retained even after removal of the applied voltage.

In such a ferroelectric capacitor, the polarity of the spontaneouspolarization is also reversed in response to the reversal of thepolarity of the applied voltage. Accordingly, the written informationmay be read by detecting this spontaneous polarization. FeRAMs operatewith lower voltage than flash memories, and enable writing informationat high speed with low power.

It is desirable to repeat heat treatment in an oxygen atmosphere in theprocess of manufacturing such FeRAMs in order to recover thecharacteristics of the ferroelectric film degraded by processing in anon-oxidizing atmosphere. Oxygen deficiencies are easily caused in theferroelectric film of the ferroelectric capacitor by processing in anon-oxidizing atmosphere, so that characteristics as a ferroelectricfilm, such as the amount of switching charge and a leak current value,may be degraded. Therefore, conventionally, a metal that is less likelyto be oxidized even in an oxygen atmosphere, such as Pt, or a conductiveoxide such as IrOx or RuOx is used as the upper electrode of theferroelectric capacitor.

In recent years, FeRAMs are no exceptions to exacting requirements formicrofabrication, so that there are also a demand for miniaturization ofthe ferroelectric capacitor and a demand for adoption of a multilayerinterconnection structure. Further, there is also a demand for FeRAMsthat operate with low voltage in view of application to portableinformation processors.

In order for FeRAMs to be operable with low voltage, the ferroelectricfilm of the ferroelectric capacitor has a large amount of switchingcharge Q_(sw). In the case of using a multilayer interconnectionstructure, however, there is the problem of the degradation of thecharacteristics of the already formed ferroelectric capacitor due to areducing atmosphere or a non-oxidizing atmosphere used in the process offorming the multilayer interconnection structure.

For example, in the case of forming the upper electrode with a Pt filmor an Ir film, there is a problem in that hydrogen in the reducingatmosphere used in forming an interlayer insulating film in themultilayer interconnection structure enters the Pt film or Ir film to beactivated through the catalysis of the metal, so that the activatedhydrogen reduces the ferroelectric film in the ferroelectric capacitor.The reduction of the ferroelectric film substantially degrades theoperating characteristics of the ferroelectric capacitor. This problemof the degradation of the characteristics of the ferroelectric film isparticularly conspicuous in the case of a miniaturized ferroelectriccapacitor having its capacitor insulating film formed of a miniaturizedferroelectric film pattern.

The following are examples of related art of the present invention:Japanese Laid-open Patent Publication No. 2004-273787, Japanese PatentNo. 3661850, Japanese Laid-open Patent Publication No. 2006-128274,Japanese Laid-open Patent Publication No. 2000-91270, Japanese Laid-openPatent Publication No. 10-242078, Japanese Laid-open Patent PublicationNo. 2001-127262, Japanese Laid-open Patent Publication No. 2002-246564,Japanese Laid-open Patent Publication No. 2005-183842, JapaneseLaid-open Patent Publication No. 2006-73648, Japanese Laid-open PatentPublication No. 2006-222227, Japanese Laid-open Patent Publication No.2000-58525, Japanese Laid-open Patent Publication No. 2003-197874,Japanese Laid-open Patent Publication No. 2002-289793, and JapaneseLaid-open Patent Publication No. 2003-347517.

SUMMARY

According to an aspect of the present invention, a semiconductor deviceincludes a substrate; and a ferroelectric capacitor formed on thesubstrate, the ferroelectric capacitor including a lower electrode; aferroelectric film formed on the lower electrode; and an upper electrodeformed on the ferroelectric film, the upper electrode including a firstlayer formed of an oxide whose stoichiometric composition is expressedas chemical formula AOx₁ using a composition parameter x₁ and whoseactual composition is expressed as chemical formula AOx₂ using acomposition parameter x₂; a second layer formed on the first layer, thesecond layer being formed of an oxide whose stoichiometric compositionis expressed as chemical formula BOy₂ using a composition parameter y₁and whose actual composition is expressed as chemical formula BOy₂ usinga composition parameter y₂; and a metal layer formed on the secondlayer, wherein the second layer is higher in ratio of oxidation than thefirst layer, the composition parameters x₁, x₂, y₁, and y₂ satisfyy₂/y₁>x₂/x₁, and the second layer includes an interface layer of thestoichiometric composition formed at an interface with the metal layer,the interface layer being higher in ratio of oxidation than a rest ofthe second layer.

According to another aspect of the present invention, a method ofmanufacturing a semiconductor device includes forming a ferroelectriccapacitor, wherein forming the ferroelectric capacitor includes forminga lower electrode; depositing a ferroelectric film on the lowerelectrode; depositing a first conductive oxide film on the ferroelectricfilm; crystallizing the first conductive oxide film in an oxidizingatmosphere; depositing a second conductive oxide film in amicrocrystalline state on the first conductive oxide film after saidcrystallizing; crystallizing a surface of the second conductive oxidefilm in an oxidizing atmosphere; and depositing a metal film on thesecond conductive oxide film after said crystallizing the surfacethereof.

The object and advantages of the embodiments will be realized andattained by means of the elements and combinations particularly pointedout in the claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and notrestrictive of the invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWING(S)

FIG. 1 is a flowchart illustrating a method of manufacturing aconventional ferroelectric capacitor;

FIG. 2 is a diagram illustrating the conventional ferroelectriccapacitor;

FIG. 3A is a diagram illustrating a ferroelectric capacitor according toa first embodiment;

FIG. 3B is another diagram illustrating the ferroelectric capacitor ofFIG. 3A according to the first embodiment;

FIG. 4 is a flowchart illustrating a process for manufacturing theferroelectric capacitor of FIG. 3A according to the first embodiment;

FIGS. 5A through 5H are diagrams illustrating the process formanufacturing the ferroelectric capacitor of FIG. 3A according to thefirst embodiment;

FIGS. 6A through 6D illustrate surface conditions of a film obtained inthe process of FIG. 5E according to the first embodiment;

FIGS. 7A through 7F illustrate surface conditions of a film obtained inthe process of FIG. 5G according to the first embodiment;

FIG. 8A is a graph illustrating a change in an X-ray diffraction causedby the heat treatment process of FIG. 5E according to the firstembodiment;

FIG. 8B is a graph illustrating a change in an X-ray diffraction causedby the heat treatment process of FIG. 5G according to the firstembodiment;

FIG. 8C is another graph illustrating a change in an X-ray diffractioncaused by the heat treatment process of FIG. 5G according to the firstembodiment;

FIG. 8D is another graph illustrating a change in an X-ray diffractioncaused by the heat treatment process of FIG. 5G according to the firstembodiment;

FIG. 9A illustrates an electrical characteristic of the ferroelectriccapacitor of FIG. 3A according to the first embodiment;

FIG. 9B illustrates an electrical characteristic of the ferroelectriccapacitor of FIG. 3A according to the first embodiment;

FIG. 10 illustrates an electrical characteristic of the ferroelectriccapacitor of FIG. 3A according to the first embodiment;

FIGS. 11A through 11V are diagrams illustrating a method ofmanufacturing a ferroelectric memory according to a second embodiment;

FIG. 12 is a diagram illustrating a method of manufacturing aferroelectric memory according to a third embodiment;

FIG. 13 is a diagram illustrating a method of manufacturing aferroelectric memory according to a variation of the third embodiment;and

FIG. 14 is a diagram illustrating a method of manufacturing aferroelectric memory according to a fourth embodiment.

DESCRIPTION OF EMBODIMENTS

As described above, in the case of forming the upper electrode with a Ptfilm or an Ir film, there is the problem of the degradation of thecharacteristics of the ferroelectric film.

Therefore, for example, Patent Document 2 listed above proposes thetechnique of configuring the upper electrode, formed on theferroelectric film, with a crystallized first conductive oxide film anda second conductive oxide film formed on the first conductive oxidefilm, where the composition of the second conductive oxide film iscloser to a stoichiometric composition than that of the first conductiveoxide film is.

FIG. 1 is a flowchart illustrating a method of manufacturing aferroelectric capacitor according to Patent Document 2.

Referring to FIG. 1, first, in step S1, a lower electrode is formed, andin step S2, a ferroelectric film such as a PZT (lead zirconate titanate)film is formed on the lower electrode.

Next, in step S3, a first conductive oxide film of an iridium oxide(IrOx) is formed on the ferroelectric film by sputtering as part of anupper electrode. Then, in step S4, the first conductive oxide film iscrystallized by being subjected to crystallizing heat treatment in acontrolled oxidizing atmosphere.

Further, in step S5, a second conductive oxide film of an iridium oxide(IrOy) is formed on the crystallized first conductive oxide film bysputtering with a higher oxidization ratio (x<y≦2). Then, in step S6, ametal electrode of 1 r is formed on the second conductive oxide film.

However, the studies that form the basis of the present invention havefound that according to the technique of Patent Document 2, since thesecond conductive oxide film is formed at low temperatures, the secondconductive oxide film is crystallized in a subsequent process such as aheat treatment process in forming a multilayer interconnectionstructure, so that the second conductive oxide film may contract tocause generation of voids as illustrated in FIG. 2.

Referring to FIG. 2, the ferroelectric capacitor is formed over a TiNorientation control film with a TiAlN oxygen barrier film interposedtherebetween. The ferroelectric capacitor is formed of the lower Irelectrode, the ferroelectric PZT film thereon, and the upper electrodelayer thereon. The upper electrode layer is formed of the firstconductive oxide film IrOx formed of an iridium oxide, the secondconductive oxide film IrOy formed on the first conductive oxide filmIrOx, and the metal (Ir) film formed on the second conductive oxide filmIrOy. The composition of the second conductive oxide film IrOy, which isalso formed of an iridium oxide, is closer to a stoichiometriccomposition than that of the first conductive oxide film IrOx is. FIG. 2illustrates multiple voids formed in the second conductive oxide filmIrOy. Further, because of the formation of these voids, voids are alsoformed at the interface of the ferroelectric PZT film and the firstconductive oxide film IrOx. On the other hand, the void at the interfacebetween the lower Ir electrode and the ferroelectric PZT film, which isa reflection (result) of the unevenness of the surface of a via plugunder the TiN orientation control film, may be eliminated byplanarization.

If voids are thus generated in the second conductive oxide film IrOy ona large scale, hydrogen enters the voids in a process conducted afterthe formation of the metal (Ir) film, such as a multilayerinterconnection structure forming process, so as to reduce the iridiumoxide or enter even the ferroelectric PZT film below the iridium oxide,thus causing the problem of the degradation of the electricalcharacteristics of the ferroelectric capacitor.

Preferred embodiments of the present invention are explained below withreference to accompanying drawings.

[a] First Embodiment

FIG. 3A is a diagram illustrating a ferroelectric capacitor 10 accordingto a first embodiment.

Referring to FIG. 3A, the ferroelectric capacitor 10 is formed on asilicon oxide film 11 covering a silicon substrate (not graphicallyillustrated). The ferroelectric capacitor 10 includes an orientationcontrol film 12 formed on the silicon oxide film 11; a conductive oxygenbarrier film 13 (a conductive oxygen diffusion barrier film) formed onthe orientation control film 12; a lower electrode 14 formed on theconductive oxygen barrier film 13; a ferroelectric film 15 (aferroelectric capacitor insulating film) formed on the lower electrode14; a first conductive oxide film 16 formed on the ferroelectric film15; a second conductive oxide film 17 formed on the first conductiveoxide film 16; a stoichiometric composition region 17A formed at thesurface of the second conductive oxide film 17; and a metal film 18formed on the second conductive oxide film 17 and in contact with thestoichiometric composition region 17A.

The orientation control film 12 is formed of a TiN film having a (111)orientation or a Ti film having a (002) orientation, and controls thecrystal orientation of the ferroelectric film 15.

The conductive oxygen barrier film 13 is formed of a TiAlN film having a(111) orientation, and prevents oxygen from entering interconnectionpatterns (not graphically illustrated) in the silicon oxide film 11.

The lower electrode 14 is formed of a Pt film having a (111)orientation. The ferroelectric film 15 is formed of a PZT film having a(111) orientation.

The first conductive oxide film 16 is formed of a first iridium (Ir)oxide crystallized film. The second conductive oxide film 17 is formedof a second iridium (Ir) oxide crystallized film.

The stoichiometric composition region 17A is formed of an iridium (Ir)oxide film of a stoichiometric composition (IrO₂) having a thickness of1 nm to 20 nm, and is higher in oxygen concentration than any otherparts of the second conductive oxide film 17. The metal film 18 isformed of an iridium (Ir) film.

The first conductive oxide film 16, the second conductive oxide film 17including the stoichiometric composition region 17A, and the metal film18 form the upper electrode of the ferroelectric capacitor 10 of FIG.3A.

FIG. 3B is a schematic diagram illustrating the distribution ofcomposition parameters x and y in the depth direction in the case ofexpressing the compositions of the first conductive oxide film 16 andthe second conductive oxide film 17 including the stoichiometriccomposition region 17A as IrOx and IrOy, respectively, using thecomposition parameters x and y.

According to this embodiment, the second conductive oxide film 17 is,after its formation, subjected to rapid heat treatment to becrystallized in an oxidizing atmosphere before formation of the metalfilm 18. Accordingly, oxygen is introduced into the second conductiveoxide film 17 simultaneously with its crystallization, so that at thesame time that the composition of the second conductive oxide film 17approaches a stoichiometric composition, a surface layer having a stablestoichiometric composition is formed at its surface portion. Therefore,even when heat treatment is performed in a process after formation ofthe metal film 18, such as a process for forming an interconnectionstructure, such formation of voids as described above with reference toFIG. 2 is prevented in the second conductive oxide film 17, so thatdegradation of the characteristics of the ferroelectric capacitor 10 dueto such void formation is avoided.

This embodiment includes such a case as indicated by a one-dot chainline in FIG. 3B, where the oxygen concentration profile in the secondconductive oxide film 17 decreases gradually in a downward directionfrom the stoichiometric composition region 17A (surface layer). In thiscase as well, the stoichiometric composition region 17A having astoichiometric composition is believed to be formed at the surface ofthe conductive oxide film 17.

FIG. 4 is a flowchart illustrating a process for manufacturing theferroelectric capacitor 10 of FIG. 3A. FIGS. 5A through 5H are diagramsillustrating the process for manufacturing the ferroelectric capacitor10 of FIG. 3A.

Referring to FIG. 5A, a Ti film having a (002) orientation is formed onthe silicon oxide film 11 covering a silicon substrate (not graphicallyillustrated) as the orientation control film 12 by sputtering. On theorientation control film 12, a TiAlN film is formed as the conductiveoxygen barrier film 13 by reactive sputtering. The silicon oxide film 11may carry an Al₂O₃ film on its surface.

For example, the Ti film (orientation control film) 12 may be formed bysupplying sputtering power of 2.6 kW for five seconds at a substratetemperature of 20° C. in an Ar atmosphere at a pressure of 0.15 Pa witha distance of 60 mm between a substrate to be processed and a target ina DC sputtering apparatus. Further, the TiAlN film (conductive oxygenbarrier film) 13 may be formed to be 100 nm in thickness by supplyingsputtering power of 1.0 kW at a substrate temperature of 400° C. whilefeeding Ar gas and nitrogen gas at flow rates of 40 sccm and 10 sccm,respectively, in an Ar/N₂ atmosphere at a pressure of 253.3 Pa using aTi—Al alloy target in the same DC sputtering apparatus.

It is preferable to nitride the Ti film 12 once after its formation. Bythus nitriding the Ti film 12, it is possible to prevent Ti from beingoxidized from film side surfaces in a recovering heat treatment of theferroelectric film 15 to be performed later.

Here, the conductive oxygen barrier film 13 is not limited (in material)to TiAlN, and may be an Ir or Ru film. The orientation control film 12is not limited (in material) to Ti or TiN, and Pt, Ir, Re, Ru, Pd, Osand alloys thereof may also be used for the orientation control film 12.Further, the orientation control film 12 may be a single layer film or alaminated (multilayer) film of Ti, Al, Ir, Pt, Ru, Pd, Os, Rh, PtOx,IrOx, RuOx, PdOx, etc.

Further, in the process of FIG. 5A, the lower electrode 14 (lowerelectrode film) of a Pt film having a thickness of approximately 100 nmis formed on the conductive oxygen barrier film 13 by sputtering withsputtering power of 0.5 kW at a substrate temperature of 400° C. in anAr atmosphere at a pressure of 0.2 Pa, for example. This corresponds tostep S11 of FIG. 4. The lower electrode 14 is not limited (in material)to pure Pt, and may be a noble metal alloy including Pt or a laminated(multilayer) film of Pt or a noble metal alloy including Pt and aplatinum oxide (PtO).

The lower electrode 14 (Pt lower electrode film) thus formed has a (111)orientation, and effectively restricts the orientation of theferroelectric film 15 to be formed thereon to a (111) orientation.

Next, in the process of FIG. 5B, a PZT film is formed as theferroelectric film 15 of 100 nm to 200 nm in thickness on the lowerelectrode 14 by high-frequency sputtering with a power of 1000 W at asubstrate temperature of 50° C. in an Ar atmosphere at a pressure of 0.9Pa using a target of a PLZT composition, for example. This correspondsto step S12 of FIG. 4. The ferroelectric film 15 thus formed is in anamorphous state, and has a PLZT composition in the case where the targetused has a PLZT composition. Alternatively, the ferroelectric film 15may be formed by MOCVD.

Next, in the process of FIG. 5C, the structure of FIG. 5B is subjectedto rapid heat treatment at a temperature lower than or equal to 650° C.in an oxygen-containing Ar atmosphere at a pressure of 0.1 MPa, so as tocompensate for oxygen deficiencies in the ferroelectric film 15.

Subsequently, the structure of FIG. 5B is further subjected to rapidheat treatment (rapid thermal annealing [RTA]) at 750° C. in an oxygenatmosphere so as to crystallize the ferroelectric film 15. This rapidheat treatment densifies the Pt film forming the lower electrode 14 soas to prevent the interdiffusion of Pt and oxygen between the lowerelectrode 14 and the ferroelectric film 15.

Next, in the process of FIG. 5D, an iridium oxide film of 20 nm to 75 nmin thickness is deposited as the first conductive oxide film 16 on theferroelectric film 15 by sputtering. This corresponds to step S13 ofFIG. 4. For example, such sputtering may be performed by feeding Ar gasand oxygen gas at flow rates of 140 sccm and 60 sccm, respectively, andinputting sputtering power of approximately 1 kW under a pressure of 0.3Pa at a temperature higher than or equal to 150° C. and lower than orequal to 350° C., for example, 300° C. The iridium oxide film 16 (thefirst conductive oxide film 16) thus formed is in a crystalline state,and has a nonstoichiometric composition IrOx whose parameter xrepresenting an oxygen composition is 1.92 (x=1.92).

Alternatively, the iridium oxide film 16 of FIG. 5D may be formed by RFsputtering at a temperature higher than or equal to 10° C. and lowerthan or equal to 50° C., for example, room temperature. In this case, Argas and oxygen gas are fed at flow rates of 100 sccm and 52 to 59 sccm,respectively, and sputtering power of approximately 2 kW under apressure of 0.23 Pa. The iridium oxide film 16 thus formed is in anamorphous state, and has a nonstoichiometric composition IrOx whosecomposition parameter x is 1.20 through 1.50.

Further, according to this embodiment, in the process of FIG. 5E, thestructure of FIG. 5D is subjected to heat treatment in a controlledoxidizing atmosphere so as to crystallize the iridium oxide film 16 inorder to prevent formation of voids in conductive oxide films formingpart of the upper electrode structure illustrated with reference to FIG.2. This corresponds to step S14 of FIG. 4.

It has been found that such heat treatment of the iridium oxide film 16in an oxidizing atmosphere deserves attention because there is likely tobe abnormal growth of iridium oxide crystal grains.

FIG. 6A is a scanning electron microscope (SEM) photograph illustratingthe surface condition of the iridium oxide film 16 in the case ofperforming such heat treatment with rapid heat treatment for 60 secondsat a temperature of 725° C. in an Ar-oxygen gas mixture atmosphere of anoxygen concentration of 1%. Likewise, FIGS. 6B, 6C, and 6D are SEMphotographs of the surface conditions of the iridium oxide films 16 inthe case of performing the same heat treatment in Ar-oxygen gas mixtureatmospheres of oxygen concentrations of 20%, 30%, and 50%, respectively.

Referring to FIGS. 6A through 6D, it is seen that within the range ofoxygen concentrations of 1% to 30%, the size of crystal grains in theiridium oxide film 16 gradually increases with an increase in the oxygenconcentration in the atmosphere, while the crystal grain size issubstantially uniform and no isolated giant crystal is generated. On theother hand, with the oxygen concentration being higher than 30%,isolated giant crystals of iridium oxide are seen as illustrated in FIG.6D.

If abnormal growth thus occurs on the surface of the iridium oxide film16, the abnormality of the surface morphology is transmitted to theiridium oxide film 17 (the second conductive oxide film 17) on theiridium oxide film 16, so that abnormality may also be caused in thesurface morphology of the iridium oxide film 17.

Therefore, it is desirable to perform the heat treatment of the processof FIG. 5E in an atmosphere of an oxygen concentration of 30% or less.On the other hand, in the case of performing the heat treatment of theprocess of FIG. 5E in an oxygen-free inert gas atmosphere, oxygen at thesurface of the iridium oxide film 16 is separated. Accordingly, anoxygen concentration of at least 0.1% is believed to be desired for theheat treatment atmosphere. Therefore, according to this embodiment, theheat treatment of the process of FIG. 5E is performed in an Ar-oxygengas mixture atmosphere of an oxygen concentration of 20%. It is believedto be preferable to perform such heat treatment with an oxygenconcentration higher than or equal to 1% and lower than or equal to 20%.

Further, at temperatures lower than 650° C., the effect of the heattreatment of the process of FIG. 5E is low, so that the ferroelectriccapacitor 10 has unsatisfactory electrical characteristics. On the otherhand, if the temperature of the heat treatment exceeds 750° C., thebarrier characteristics of the TiAlN conductive oxygen barrier film 13under the lower electrode 24 may be degraded. Accordingly, thetemperature of the heat treatment is preferably higher than or equal to650° C. and lower than or equal to 750° C. Therefore, according to thisembodiment, the heat treatment (of the process of FIG. 5E) is performedwith rapid heat treatment for 60 seconds at a temperature of 725° C. inan Ar-oxygen gas mixture atmosphere of an oxygen concentration of 20%.

According to this embodiment, the iridium oxide film 16 has anonstoichiometric composition as described above. Accordingly, as aresult of the heat treatment of FIG. 5E, Pb is diffused from the PZTfilm forming the ferroelectric film 15 into the iridium oxide (IrOx)film 16, so that a flat interface is formed between the ferroelectricfilm 15 and the iridium oxide film 16. As a result, on application ofvoltage to the ferroelectric capacitor 10, a uniform electric field isinduced in the ferroelectric film 15 so as to allow polarizationreversal to be induced in the ferroelectric capacitor 10 at low drivevoltage.

Next, according to this embodiment, in the process of FIG. 5F, theiridium oxide film 17 is formed to be 100 nm to 150 nm in thickness onthe structure of FIG. 5E by sputtering at a substrate temperature higherthan or equal to 50° C. and lower than or equal to 80° C. The iridiumoxide film 17 thus formed is in a microcrystalline state. Thiscorresponds to step S15 of FIG. 4. If the iridium oxide film 17 thusformed is in an amorphous state, the iridium oxide film 17 becomesnon-uniform after crystallization in the subsequent process in which theiridium oxide film 17 is subjected to crystallization heat treatment, sothat voids described with reference to FIG. 2 are likely to be generatedin the iridium oxide film 17. Further, if the iridium oxide film 17 isformed at a temperature higher than or equal to 150° C., some crystalgrains grow abnormally so as to prevent a flat surface morphology frombeing obtained although the obtained iridium oxide film 17 is in acrystallized state. Further, the obtained iridium oxide film 17 includesboth microcrystals and crystals if the film formation temperature islower than or equal to 100° C., and is formed of only microcrystals ifthe film formation temperature is lower than or equal to 80° C.Therefore, according to this embodiment, the film formation process ofFIG. 5F by sputtering is performed at a temperature higher than or equalto 50° C. and lower than or equal to 80° C., for example, 60° C.

At this point, in the process of FIG. 5F, the iridium oxide film 17 isformed by sputtering by feeding Ar gas and oxygen gas at flow rates of100 sccm and 100 sccm, respectively, and inputting sputtering power of,for example, 1 kW under a pressure of 0.3 Pa. In the case of forming theiridium oxide film 17 under these conditions, it is possible to preventabnormal oxidation and the resultant abnormal growth of crystal grainson the surface of the iridium oxide film 17.

Next, in the process of FIG. 5G, which corresponds to step S16 of FIG.4, the structure of FIG. 5F is crystallized by being subjected to rapidheat treatment (rapid thermal annealing [RTA]) for 60 seconds at atemperature within the range of 650° C. to 750° C., for example, 700°C., under normal pressure or reduced pressure in an Ar-oxygen gasmixture atmosphere.

FIGS. 7A, 7B, 7C, 7D, 7E, and 7F are metallurgical microscopephotographs observing the surface conditions of the obtained iridiumoxide films 17 in the case of performing the heat treatment of FIG. 5Gin Ar-oxygen gas mixture atmospheres with oxygen concentrations of 1%,10%, 20%, 25%, 30%, and 50%, respectively, at a pressure of 0.1 MPa.

Referring to FIGS. 7A through 7E, uniform surface conditions areobserved up to an oxygen concentration of 30%. However, with an oxygenconcentration higher than 30%, a non-uniform structure is observed andit is seen that abnormal growth is caused on the surface as in FIG. 7F.

Therefore, according to this embodiment, the heat treatment process ofFIG. 5G is performed with an oxygen concentration higher than or equalto 0.1% and lower than or equal to 30%, preferably an oxygenconcentration higher than or equal to 1% and lower than or equal to 20%,the same as in the heat treatment process of FIG. 5E, so as to avoidsuch a problem of abnormal growth.

FIGS. 8A, 8B, and 8C are graphs representing X-ray diffraction patternsof the first iridium oxide film 16, the second iridium oxide film 17,and the laminated structure of the first and second iridium oxide films16 and 17, respectively.

Referring to FIG. 8A, the solid line corresponds to the condition of theiridium oxide film 16 immediately after its formation, and the brokenline corresponds to the condition of the iridium oxide film 16 afterbeing subjected to the heat treatment process of FIG. 5E. When these arecompared, it is found that the heat treatment of FIG. 5E hardly causesany change to the diffraction pattern in each of the peak position andthe 2θ angle and that diffraction peaks also substantially coincide withthe diffraction peaks of the IrO₂ film, which is of a stoichiometriccomposition. This indicates that the iridium oxide film 16 has beencrystallized completely by the heat treatment process of FIG. 5E.

FIG. 8B is a graph presenting the X-ray diffraction patterns of theindependently formed iridium oxide film 17 immediately after itsformation (broken line) and after being subjected to the heat treatmentof FIG. 5G in an atmosphere of an oxygen concentration of 1% (solidline) in a comparative manner. In this case, immediately after the filmformation, the film 17 is in a microcrystalline state with the (110) and(200) diffraction peaks being low and the 2θ angle being shifted to thelower angle side compared with that of IrO₂. On the other hand, it isseen that after the heat treatment, the film 17 is completelycrystallized and the (110) and (200) diffraction peaks substantiallymatch the corresponding (110) and (200) peaks of the stoichiometriccomposition IrO₂ film.

Further, FIG. 8C is a graph representing the X-ray diffraction patternsof the multilayer structure of the iridium oxide films 16 and 17 asillustrated in FIG. 5G before and after the heat treatment of FIG. 5G ina comparative manner. In FIG. 8C, the broken line corresponds to thecondition before the heat treatment process of FIG. 5G, and the solidline corresponds to the condition after the heat treatment process ofFIG. 5G.

Referring to FIG. 8C, in this experiment, substantially the same resultsas those of FIG. 8B were obtained. That is, immediately after theformation of the iridium oxide film 17, the film 17 is in amicrocrystalline state with the (110) and (200) diffraction peaks beinglow and the 2θ angle being shifted to the lower angle side compared withthat of IrO₂. On the other hand, it is seen that after the heattreatment of FIG. 5G, the iridium oxide film 17 is completelycrystallized and the (110) and (200) diffraction peaks substantiallymatch the corresponding (110) and (200) peaks of the stoichiometriccomposition IrO₂ film.

Further, FIG. 8D illustrates the case of varying the oxygenconcentration in the atmosphere in subjecting the iridium oxide film 17independently to heat treatment corresponding to the process of FIG. 5G.

It is seen from FIG. 8D that as the oxygen concentration in theatmosphere increases, the Ir (110) peak decreases and the Ir (200) peakincreases. This means that the heat treatment has increased the degreeof oxidation of the iridium oxide film 17.

That is, it is believed as follows. The iridium oxide film 17 is low inthe degree of oxidation and its composition deviates greatly from theideal stoichiometric composition IrO₂ in a microcrystalline stateimmediately after its formation. On the other hand, the heat treatmentof FIG. 5G causes oxygen to be taken into the iridium oxide film 17 fromthe atmosphere so as to increase the in-film oxygen composition (value)y. At this point, the oxygen composition y is maximized, in particular,at the film surface, so that the stoichiometric composition region 17A(surface region) of 20 nm or less in thickness having a stoichiometriccomposition IrO₂ is formed. As a result, the oxygen concentrationprofile illustrated in FIG. 3B is generated in the upper electrodestructure of the ferroelectric capacitor 10 including the iridium oxidefilms 16 and 17.

Table 1 below illustrates a collection of data on the oxygen compositionparameters x and y after the heat treatment process of FIG. 5G, obtainedby HRBS (high-resolution Rutherford backscattering spectrometry) withrespect to the first iridium oxide (IrOx) film 16 and the second iridiumoxide (IrOy) film 17 thus formed.

TABLE 1 FILM FILM FORMATION HRBS CONDUCTIVE FORMATION GAS Ar:O₂ RESULTSOXIDE FILM TEMPERATURE (Sccm) x, y IrOx 20° C. 100:52  1.20 IrOx 20° C.100:59  1.50 IrOx 300° C.  140:60  1.92 IrOy 20° C. 100:100 2.10 IrOy60° C. 100:100 2.10 IrOy 300° C.  100:100 2.05

Referring to Table 1, the oxygen composition parameter x of the firstiridium oxide film 16 has a value of 1.20 to 1.50 when formed at asubstrate temperature of 20° C. and a value of 1.92 when formed at asubstrate temperature of 300° C., and the oxygen composition parameter yof the second iridium oxide film 17 has a value of 2.10 when formed at asubstrate temperature of 20° C. to 60° C. and a value of 2.05 whenformed at a substrate temperature of 300° C.

Here, it is believed that as described above, oxygen is introduced intothe iridium oxide film 17 from its surface by the heat treatment in theprocess of FIG. 5G so that while the iridium oxide film 17 has asubstantially stoichiometric composition IrO₂ at its surface, the oxygenconcentration is reduced inside the film 17, thus resulting in theoxygen distribution described above with reference to FIG. 3B.

Next, in the process of FIG. 5H, which corresponds to step S17 of FIG.14, the metal Ir film 18 is formed on the iridium oxide film 17 of FIG.5G, so that the ferroelectric capacitor 10 is completed.

FIGS. 9A and 9B illustrate the amount of switching charge Q_(sw) and theleak current density, respectively, of the ferroelectric capacitor 10thus obtained. FIGS. 9A and 9B illustrate the case where theferroelectric capacitor 10 is 50 μm×50 μm in size and the measurementswere performed with a multilayer interconnection structure of fivelayers on the ferroelectric capacitor 10. In FIGS. 9A and 9B, TEL-AN1indicates the oxygen concentration in the atmosphere in the heattreatment process of FIG. 5E, and TEL-AN2 indicates the oxygenconcentration in the atmosphere in the heat treatment process of FIG.5G.

Referring to FIG. 9A, according to this embodiment, values greater thanor equal to 28 μC/cm² are obtained as the amount of switching chargeQ_(sw). These values are far greater than the value (28 μC/cm²) obtainedin Patent Document 2. Further, it is seen from FIG. 9B that the leakcurrent may be substantially reduced particularly in the case ofperforming the heat treatment process of FIG. 5G with oxygenconcentrations higher than or equal to 10%. This indicates that theformation of voids described above with reference to FIG. 2 iscontrolled effectively in the iridium oxide film 17. On the other hand,a large leak current is generated in the case of an oxygen concentrationof 1% in the heat treatment process of FIG. 5G. This indicates that thevoids described above with reference to FIG. 2 are generated on a largescale in the iridium oxide film 17.

Further, FIG. 10 illustrates the relationship between the amount ofswitching charge Q_(sw) and the applied voltage of the ferroelectriccapacitor 10 thus obtained.

Referring to FIG. 10, the relationship between the amount of switchingcharge Q_(sw) and the applied voltage is affected by the heat treatmentprocess of FIG. 5E and the heat treatment process of FIG. 5G. Byperforming these heat treatment processes with an oxygen concentrationof 20%, the relationship may be changed so as to cause the amount ofswitching charge Q_(sw) to rise sharply. According to this embodiment,by thus performing the heat treatment processes of FIGS. 5E and 5G in anatmosphere of a relatively high oxygen concentration, it is possible tocontrol formation of voids in the iridium oxide film 17, so that theproblem of entrance of hydrogen or water into a ferroelectric capacitoris solved even when the subsequent process of forming a multilayerinterconnection structure is performed.

According to this embodiment, in forming the ferroelectric capacitor 10of FIG. 3A, the heat treatment processes of FIGS. 5E and 5G areperformed in an Ar-oxygen gas mixture atmosphere of an oxygenconcentration of 30% or less. As a result, it is possible to avoidabnormal growth of iridium oxide crystals on the surfaces of the firstand second iridium oxide films 16 and 17. In the processes of FIGS. 5Eand 5G, the Ar gas may be replaced with other inert gases such asnitrogen gas and He gas. Further, the oxygen gas may be replaced withother oxidizing gases such as N₂O and ozone.

In this embodiment, after step S12 of FIG. 4, a thinner amorphousferroelectric film may be formed on the crystallized ferroelectric film15 to compensate for oxygen deficiencies, and thereafter or immediatelythereafter, the first iridium oxide film 16 may be formed thereon.

Further, after step S16 and before step S17 of FIG. 4, further rapidheat treatment may be performed at 650° C. to 750° C. so as to increasethe adhesion between the ferroelectric film 15 and the upper electrode(the first and second iridium oxide films 16 and 17).

According to this embodiment, the first and second conductive oxidefilms 16 and 17 are described as iridium oxide films. However, thisembodiment is not limited to such a particular material, and materialssuch as a ruthenium oxide, a rhodium oxide, a rhenium oxide, and anosmium oxide may also be used for the first and second conductive oxidefilms 16 and 17. These conductive oxide films may be formed bysputtering using metal elements such as Ir, Ru, Rh, Re, and Os astargets.

[b] Second Embodiment

A description is given, with reference to FIGS. 11A through 11V, of aprocess for manufacturing a ferroelectric memory according to a secondembodiment of the present invention.

Referring to FIG. 11A, an n-type well is formed as a device region 61Ain a silicon substrate 61. A first MOS transistor 60A and a second MOStransistor 60B are formed on the device region 61A. The first MOStransistor 60A includes a gate insulating film 62A on the siliconsubstrate 61 and a polysilicon gate electrode 63A on the gate insulatingfilm 62A. The second MOS transistor 60B includes a gate insulating film62B on the silicon substrate 61 and a polysilicon gate electrode 63B onthe gate insulating film 62B.

P⁻-type LDD regions 61 a and 61 b are formed in the silicon substrate 61in correspondence to the sidewall faces of the gate electrode 63A.P⁻-type LDD regions 61 c and 61 d are formed in the silicon substrate 61in correspondence to the sidewall faces of the gate electrode 63B. Here,the first and second MOS transistors 60A and 60B are formed so as toshare the same p⁻-type diffusion regions as the LDD region 61 b and theLDD region 61 c in the device region 61A.

Silicide layers 64A and 64B are formed on the polysilicon gateelectrodes 63A and 63B, respectively. Further, sidewall insulating films50A and 50B are formed on the sidewall faces of the polysilicon gateelectrodes 63A and 63B, respectively.

Further, p⁺-type diffusion regions 61 e and 61 f are formed in thesilicon substrate 61 outside the sidewall insulating films 50A of thegate electrode 63A. Further, p⁺-type diffusion regions 61 g and 61 h areformed in the silicon substrate 61 outside the sidewall insulating films50B of the gate electrode 63B. The diffusion regions 61 f and 61 g areformed of the same p⁺-type diffusion region.

A SiON film 65 of, for example, 200 nm in thickness is formed on thesilicon substrate 61 so as to cover the gate electrode 63A including thesilicide layer 64A and the sidewall insulating films 50A and the gateelectrode 63B including the silicide layer 64B and the sidewallinsulating films 50B. A SiO₂ interlayer insulating film 66 of, forexample, 1000 nm in thickness is formed on the SiON film 65 by plasmaCVD using TEOS as a material. Further, the interlayer insulating film 66is flattened by CMP, and contact holes 66A, 66B, and 66C are formed inthe interlayer insulating film 66 so as to expose the diffusion regions61 e, 61 f and 61 g, and 61 h, respectively. Tungsten (W) via plugs 67A,67B, and 67C are formed on adhesion layers 67 a, 67 b, and 67 c in thecontact holes 66A, 66B, and 66C, respectively. Each of the adhesionlayers 67 a, 67 b, and 67 c has a multilayer structure of a Ti film of30 nm in thickness and a TiN film of 20 nm in thickness.

Further, according to the structure of FIG. 11A, another SiON film 67of, for example, 130 nm in thickness is formed on the interlayerinsulating film 66, and another interlayer insulating film 68 of asilicon oxide film of, for example, 300 nm in thickness is formed on theSiON film 67 by plasma CVD using TEOS as a material the same as theinterlayer insulating film 66. Here, the SiON film 67 may be replacedwith a SiN film or an Al₂O₃ film.

Next, in the process of FIG. 11B, via holes 68A and 68C are formed inthe interlayer insulating film 68 so as to expose the via plugs 67A and67C, respectively. A tungsten via plug 69A is formed on an adhesionlayer 69 a in the via hole 68A so as to come into contact with the viaplug 67A. The adhesion layer 69 a has a multilayer structure of a Tifilm and a TiN film the same as the adhesion layer 67 a. Further, atungsten via plug 69C is formed on an adhesion layer 69 c in the viahole 68C so as to come into contact with the via plug 67C. The adhesionlayer 69 c has a multilayer structure of a Ti film and a TiN film thesame as the adhesion layer 67 c.

Next, in the process of FIG. 1C, the surface of the interlayerinsulating film 68 is processed with NH₃ plasma so as to cause NH groupsto be bound with oxygen atoms at the surface of the interlayerinsulating film 68. Then, a Ti film 70 of, for example, 20 nm inthickness is formed on the interlayer insulating film 68 by sputteringso as to cover the via plugs 69A and 69B. By thus processing the surfaceof the interlayer insulating film 68 with a NH₃ plasma, oxygen atoms atthe surface of the interlayer insulating film 68 are terminated by NHgroups and bound preferentially with Ti atoms so as not to restrict theorientation of the Ti film 70. Therefore, the Ti film 70 has an ideal(002) orientation.

Further, in the process of FIG. 11C, the Ti film 70 is subjected torapid heat treatment at 650° C. in a nitrogen atmosphere so as to beconverted into a TiN film having a (111) orientation. Hereinafter, thisTiN film may also be referred to by the same reference numeral as the Tifilm 70.

Next, in the process of FIG. 11D, a TiAlN film 71 is formed as an oxygendiffusion barrier on the TiN film 70. Further, in the process of FIG.1E, an Al₂O₃ film 72 having a film thickness more than or equal to 1 nmand less than or equal to 5 nm is formed as a Pb diffusion barrier filmon the TiAlN film 71 by sputtering or by oxidizing the TiAlN film 71.

Next, in the process of FIG. 11F, a Pt film of approximately 100 nm inthickness is stacked on the Al₂O₃ film 72 by sputtering, so that a lowerelectrode layer 73 is formed (on the Al₂O₃ film 72).

Next, the structure of FIG. 11F is subjected to heat treatment at atemperature higher than or equal to 650° C. for 60 seconds in an Aratmosphere. Subsequently, in the process of FIG. 11G, a first PZT film74 having a thickness of 1 nm to 50 nm, preferably, 20 nm to 30 nm, isformed on the lower electrode layer 73 by sputtering.

Next, in the process of FIG. 11H, a second PZT film 75 of, for example,80 nm in thickness is formed on the first PZT film 74 by MOCVD.

Further, in the process of FIG. 11I, in an atmosphere including oxygen,for example, a gas mixture atmosphere of oxygen gas and an inert gassuch as Ar gas, the PZT films 74 and 75 are subjected to heat treatmentfor 30 to 120 seconds, for example, 90 seconds, while feeding, forexample, oxygen gas and Ar gas at flow rates of 0 sccm to 25 sccm and2000 sccm, respectively, at a temperature of 550° C. to 800° C., forexample, 580° C., so that the PZT films 74 and 75 are crystallized. As aresult of the crystallization heat treatment of the PZT films 74 and 75,columnar PZT crystals having a (110) orientation grow upward from thesurface of the lower electrode 73 in the PZT films 74 and 75.

Next, in the process of FIG. 11J, an upper electrode layer (film) 76having a laminated (multilayer) structure of the first iridium oxidefilm 16, the second iridium oxide film 17, and the metal iridium film 18(not graphically illustrated) of the first embodiment is formed on thePZT film 75 by sputtering and heat treatment in a controlled oxidizingatmosphere in the same manner as in FIGS. 5D through 5H of the firstembodiment. Further, in the process of FIG. 11K, a TiAlN film 77 and asilicon oxide film 78 are formed as hard mask layers on the upperelectrode layer 76 by reactive sputtering and plasma CVD using a TEOSmaterial, respectively.

Further, in the process of FIG. 11L, the silicon oxide film 78 and theunderlying TiAlN film 77 are patterned, so that hard mask patterns 78Aand 78C corresponding to desired ferroelectric capacitors C₁ and C₂,respectively, are formed.

Further, in the next process of FIG. 11M, the TiAlN film 77, the upperelectrode layer 76, the PZT films 74 and 75, the lower electrode layer73, and the Al₂O₃ film 72 are patterned by dry etching using HBr, O₂,Ar, and C₄F₈ using the hard mask patterns 78A and 78C as a mask untilthe TiAlN film 71 is exposed. As a result, a multilayer structure of anAl₂O₃ pattern 72A, a lower electrode pattern 73A, PZT patterns 74A and75A, an upper electrode pattern 76A, and a TiAlN mask pattern 77A isformed under the hard mask pattern 78A in correspondence to theferroelectric capacitor C₁, and a multilayer structure of an Al₂O₃pattern 72C, a lower electrode pattern 73C, PZT patterns 74C and 75C, anupper electrode pattern 76C, and a TiAlN mask pattern 77C is formedunder the hard mask pattern 78C in correspondence to the ferroelectriccapacitor C₂. Here, the lower electrode pattern 73A, the PZT patterns74A and 75A, and the upper electrode pattern 76A form the ferroelectriccapacitor C₁, and the lower electrode pattern 73C, the PZT patterns 74Cand 75C, and the upper electrode pattern 76C form the ferroelectriccapacitor C₂.

Next, in the process of FIG. 11N, the hard mask patterns 78A and 78C areremoved by dry etching or wet etching. Then, in the process of FIG. 11O,the TiN film 70 on the interlayer insulating film 68 and the TiAlN film71 on the TiN film 70 are removed by dry etching using the ferroelectriccapacitors C₁ and C₂ as a mask. As a result, a multilayer structure of aTiN pattern 70A and the TiAlN pattern 71A is formed under the Al₂O₃pattern 72A in the ferroelectric capacitor C₁, and a multilayerstructure of a TiN pattern 70C and the TiAlN pattern 71C is formed underthe Al₂O₃ pattern 72C in the ferroelectric capacitor C₂.

Further, in the process of FIG. 11P, a very thin Al₂O₃ film 79 having athickness of 20 nm or less is formed as a hydrogen barrier film bysputtering or atomic layer deposition (ALD) so as to continuously coverthe part of the interlayer insulating film 68 exposed in theabove-described process of FIG. 11O and the upper and sidewall faces ofthe ferroelectric capacitors C₁ and C₂. Next, in the process of FIG.11Q, by performing heat treatment at a temperature of 550° C. to 750°C., for example, 650° C., in an oxygen atmosphere, the PZT films 74A and75A in the ferroelectric capacitor C₁ and the PZT films 74C and 75C inthe ferroelectric capacitor C₂ are caused to recover from such damage assuffered in the dry etching process of FIG. 11O.

Further, in the process of FIG. 11R, another Al₂O₃ film 80 of, forexample, 20 nm in thickness is formed as a hydrogen barrier film as wellon the Al₂O₃ film 79 of FIG. 11P by MOCVD. Further, in the process ofFIG. 11S, an interlayer insulating film 81 of a silicon oxide filmhaving a thickness of 1500 nm is formed by plasma CVD using TEOS and agas mixture of oxygen and helium as a material so as to cover the Al₂O₃hydrogen barrier films 79 and 80 thus formed. In the process of FIG.11S, the surface of the interlayer insulating film 81 thus formed isflattened by CMP, and thereafter, heat treatment is performed in aplasma using N₂O or nitrogen gas so as to dehydrate the interlayerinsulating film 81. Further, in the process of FIG. 11S, an Al₂O₃ film82 of 20 nm to 100 nm in thickness is formed as a hydrogen barrier filmon the interlayer insulating film 81 by sputtering or MOCVD. In theprocess of FIG. 11S, as a result of the planarization (flattening)process by CMP, the interlayer insulating film 81 has a thickness of,for example, 700 nm.

Next, in the process of FIG. 11T, an interlayer insulating film 83 of asilicon oxide film of 300 nm to 500 nm in thickness is formed on theAl₂O₃ hydrogen barrier film 82 by plasma CVD using TEOS as a material.Then, in the process of FIG. 11U, via holes 83A and 83C are formed inthe interlayer insulating film 83 so as to expose the upper electrodepattern 76A of the ferroelectric capacitor C₁ and the upper electrodepattern 76C of the ferroelectric capacitor C₂, respectively.

Further, in the process of FIG. 11U, heat treatment is performed throughthe via holes 83A and 83C thus formed in an oxidizing atmosphere so asto compensate for oxygen deficiencies caused in the PZT films 74A and75A and the PZT films 74C and 75C by the via hole forming process.

Next, the bottom and inner wall surfaces of the via hole 83A and thebottom and inner wall surfaces of the via hole 83C are covered withbarrier metal films 84 a and 84 c, respectively, each formed of a TiNsingle layer film. Further, the via holes 83A and 83C are filled withtungsten plugs 84A and 84C, respectively.

Further, after formation of the tungsten plugs 84A and 84C, a via hole83B is formed through the interlayer insulating film 83, the Al₂O₃hydrogen barrier film 82, the interlayer insulating film 81, the Al₂O₃hydrogen barrier films 79 and 80, the interlayer insulating film 68, andthe SiON film 67 so as to expose the via plug 67B, and is filled with atungsten via plug 84B. As usual, the tungsten via plug 84B is formed onan adhesion layer 84 b having a Ti/TiN multilayer structure.

Further, in the process of FIG. 11V, on the interlayer insulating film83, an interconnection pattern 85A of an AlCu alloy held betweenadhesion films 85 a and 85 d each having a Ti/TiN multilayer structureis formed in correspondence to the via plug 84A, an interconnectionpattern 85B of an AlCu alloy held between adhesion films 85 b and 85 eeach having a Ti/TiN multilayer structure is formed in correspondence tothe via plug 84B, and an interconnection pattern 85C of an AlCu alloyheld between adhesion films 85 c and 85 f each having a Ti/TiNmultilayer structure is formed in correspondence to the via plug 84C.

Another interconnection layer may be formed on the structure of FIG. 11Vas required.

According to this embodiment, the PZT patterns 74A and 75A and the PZTpatterns 74C and 75C are formed as ferroelectric films. As describedabove, in the case of forming the lower PZT patterns (lowerferroelectric films) 74A and 74C by sputtering, the PZT films formingthe lower PZT patterns 74A and 74C may include elements such as Ca andSr. Further, the PZT patterns (films) 74A, 75A, 74C, and 75C may bereplaced with PLZT films including La.

Further, in the above-described processes of FIGS. 11G and 11H, the PZTfilms 74 and 75 may be formed as a single PZT film by sputtering as inthe first embodiment.

Further, the PZT patterns (films) 74A, 75A, 74C, and 75C are not limitedto PZT films, and may be formed of any ferroelectric films having anABO₃-type perovskite structure including Pb. Examples of metal elementsthat may occupy the A site include Bi, Pb, Ba, Sr, Ca, Na, K, and rareearth elements, and examples of metal elements that may occupy the Bsite include Ti, Zr, Nb, Ta, W, Mn, Fe, Co, and Cr.

Further, the lower electrode patterns 73A and 73C are not limited to aPt film, and may be formed of an alloy including Pt or a multiplayerstructure of platinum oxide (PtO) and Pt or an alloy including Pt.

Further, the conductive oxygen barrier films (71A and 71C) are notlimited to TiAlN films, and may be Ir or Ru films.

Further, the orientation control films (70A and 70C) are not limited toa Ti or TiN film, and may be formed of any of Pt, Ir, Re, Ru, Pd, and Osfilms and alloys of two or more of the elements forming these films.Further, each of the orientation control films 70A and 70C may be formedof a single layer film or a multilayer film of Ti, Al, Ir, Pt, Ru, Pd,Os, Rh, PtOx, IrOx, RuOx, PdOx, etc.

[c] Third Embodiment

FIG. 12 is a diagram illustrating a ferroelectric memory according to athird embodiment of the present invention. In FIG. 12, the same elementsas those described above are referred to by the same reference numerals,and a description thereof is omitted.

In the second embodiment described above with reference to FIGS. 11Athrough 11V, in the process of FIG. 11B, the via plugs 69A and 69C areformed by removing an excessive tungsten film on the interlayerinsulating film 68 by CMP after filling the via holes 68A and 68C with atungsten film. According to CMP, the surfaces of the via plugs 69A and69C may not be flattened completely, so that recesses having a depth of20 nm to 50 nm may be formed at the top of the via plugs 69A and 69C.

According to this embodiment, in order to prevent such recesses fromaffecting the crystal orientation of a ferroelectric capacitor to beformed thereon, after the process of FIG. 11B and before the process ofFIG. 11C, a Ti film of a (002) orientation is deposited on theinterlayer insulating film 68 so as to fill in the recesses, and afterconversion into a TiN film of a (111) orientation by nitriding, thesurface of the TiN film is flattened by CMP. The TiN film thus formed issubjected to dry etching along with the TiN film 70 and the TiAlN film71 in the process of FIG. 11O.

As a result, in the ferroelectric memory of FIG. 12, a TiN film 70 a ofa (111) orientation is interposed between the interlayer insulating film68 and the TiN pattern (film) 70A so as to fill in the possible recessesat the top of the via plug 69A, and a TiN film 70 c of a (111)orientation is interposed between the interlayer insulating film 68 andthe TiN pattern (film) 70C so as to fill in the possible recesses at thetop of the via plug 69C.

According to this embodiment, even if recesses are formed at the top ofthe via plugs 69A and 69C in the CMP process, the above-describedconfiguration makes it possible to ensure that the orientation of theferroelectric films (PZT patterns 74A, 75A, 74C, and 75C) is restrictedto a (111) direction.

FIG. 13 is a diagram illustrating a ferroelectric memory according to avariation of this embodiment. In FIG. 13, the same elements as thosedescribed above are referred to by the same reference numerals, and adescription thereof is omitted.

Referring to FIG. 13, according to this variation, the TiN films 70 aand 70 c have their respective portions above the level of theinterlayer insulating film 68 removed at the time of flattening the TiNfilms 70 a and 70 c by CMP, so that the TiN films 70 a and 70 c remainonly in the via holes 68A and 68C, respectively.

Otherwise, the configuration of FIG. 13 is the same as that of FIG. 12,so that a description thereof is omitted.

[d] Fourth Embodiment

FIG. 14 is a diagram illustrating a ferroelectric memory according to afourth embodiment of the present invention.

Referring to FIG. 14, according to this embodiment, immediately afterforming the interlayer insulating film 81 in the process of FIG. 11Safter the process of FIG. 11R, a via hole is formed through theinterlayer insulating film 81, the Al₂O₃ hydrogen barrier films 79 and80, the interlayer insulating film 68, and the SiON film 67 so as toexpose the via plug 67B, and the via hole is filled with a tungstenfilm, so that the above-described via plug 84B is formed.

After formation of the via plug 84B, an oxygen barrier film such as aSiON film is formed on the interlayer insulating film 81. Then, in thiscondition, contact holes are formed in the interlayer insulating film 81so as to expose the upper electrode pattern 76A of the ferroelectriccapacitor C₁ and the upper electrode pattern 76C of the ferroelectriccapacitor C₂.

Further, the PZT patterns (films) 74A and 75A in the ferroelectriccapacitor C₁ and the PZT patterns (films) 74C and 75C in theferroelectric capacitor C₂ are subjected to heat treatment through thecorresponding contact holes in an oxygen atmosphere so as to compensatefor oxygen deficiencies. Thereafter, the oxygen barrier film is removed,and the electrode patterns 85A, 85B, and 85C are formed on theinterlayer insulating film 81 in correspondence to the upper electrodepattern 76A of the ferroelectric capacitor C₁, the via plug 84B, and theupper electrode pattern 76C of the ferroelectric capacitor C₂,respectively.

According to an aspect of the present invention, a first conductiveoxide film having a nonstoichiometric composition is used as an upperelectrode lower layer in contact with a ferroelectric film forming thecapacitor insulating film of a ferroelectric capacitor. As a result, Pbis diffused into the upper electrode lower layer from the ferroelectricfilm, which is accompanied by the flattening of the interface betweenthe ferroelectric film and the upper electrode lower layer.Consequently, in the case of applying voltage to the ferroelectriccapacitor, a greater effective voltage is applied to the ferroelectricfilm to improve the characteristics of the capacitor. On the other hand,when exposed to an atmosphere including hydrogen, such a conductive filmhaving a nonstoichiometric composition has its metal component insidethe film activate the hydrogen, so that the activated hydrogen degradesthe characteristics of the ferroelectric film. Therefore, according toan aspect of the present invention, an upper electrode upper layer of asecond conductive oxide film having a stoichiometric composition or acomposition closer thereto is formed on the upper electrode lower layerso as to prevent a reduction atmosphere from entering the upperelectrode lower layer.

At this point, according to an aspect of the present invention, theupper electrode upper layer formed on the upper electrode lower layerthat has been crystallized by heat treatment is in a microcrystallinestate, and the upper electrode upper layer is subjected to rapid heattreatment in an oxidizing atmosphere to be crystallized before a metalelectrode film is formed on the upper electrode upper layer. As aresult, even when the ferroelectric capacitor is subjected to heattreatment in the subsequent semiconductor device manufacturing process,generation of voids in the upper electrode upper layer is controlled,and, for example, even when a multilayer interconnection structure isformed on the ferroelectric capacitor, the problem of degradation of theelectrical characteristics of the ferroelectric capacitor due to entryof hydrogen in a reduction atmosphere to be used into the ferroelectriccapacitor through such voids is eliminated. Further, it is possible tocontrol abnormal growth on the surfaces of the upper electrode lowerlayer and the upper electrode upper layer by optimizing the ratio ofoxygen gas in a process atmosphere and temperature at the time ofperforming crystallization heat treatment on the upper electrode lowerlayer and the upper electrode upper layer.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority orinferiority of the invention. Although the embodiments of the presentinventions have been described in detail, it should be understood thatvarious changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention. Forexample, in the above-described embodiments, the present invention isapplied to a stack structure. However, the present invention may also beapplied to a planar structure.

1. A semiconductor device, comprising: a substrate; and a ferroelectriccapacitor formed on the substrate, the ferroelectric capacitor includinga lower electrode; a ferroelectric film formed on the lower electrode;and an upper electrode formed on the ferroelectric film, the upperelectrode including a first layer formed of an oxide whosestoichiometric composition is expressed as chemical formula AOx₁ using acomposition parameter x₁ and whose actual composition is expressed aschemical formula AOx₂ using a composition parameter x₂; a second layerformed on the first layer, the second layer being formed of an oxidewhose stoichiometric composition is expressed as chemical formula BOy₁using a composition parameter y₁ and whose actual composition isexpressed as chemical formula BOy₂ using a composition parameter y₂; anda metal layer formed on the second layer, wherein the second layer ishigher in ratio of oxidation than the first layer, the compositionparameters x₁, x₂, y₁, and y₂ satisfy y₂/y₁>x₂/x₁, and the second layerincludes an interface layer of the stoichiometric composition formed atan interface with the metal layer, the interface layer being higher inratio of oxidation than a rest of the second layer.
 2. The semiconductordevice as claimed in claim 1, wherein a metal element of the first layeris equal to a metal element of the second layer.
 3. The semiconductordevice as claimed in claim 1, wherein the first and second layers areformed of an iridium oxide.
 4. The semiconductor device as claimed inclaim 1, wherein a metal element of the first layer is different from ametal element of the second layer.
 5. The semiconductor device asclaimed in claim 1, wherein an interface between the ferroelectric filmand the first layer is flat.
 6. The semiconductor device as claimed inclaim 1, wherein the first layer includes Pb and the second layer issubstantially free of Pb.
 7. The semiconductor device as claimed inclaim 1, further comprising: an insulating film covering theferroelectric capacitor; and an interconnection structure formed on theinsulating film, wherein the metal layer is connected to aninterconnection pattern in the interconnection structure through acontact hole.
 8. A method of manufacturing a semiconductor device, themethod including forming a ferroelectric capacitor, wherein: saidforming the ferroelectric capacitor includes forming a lower electrode;depositing a ferroelectric film on the lower electrode; depositing afirst conductive oxide film on the ferroelectric film; crystallizing thefirst conductive oxide film in an oxidizing atmosphere; depositing asecond conductive oxide film in a microcrystalline state on the firstconductive oxide film after said crystallizing; crystallizing a surfaceof the second conductive oxide film in an oxidizing atmosphere; anddepositing a metal film on the second conductive oxide film after saidcrystallizing the surface thereof.
 9. The method as claimed in claim 8,wherein each of said crystallizing the first conductive oxide film andsaid crystallizing the surface of the second conductive oxide film isperformed with a rapid heat treatment process with a ratio of anoxidizing gas in the oxidizing atmosphere being less than or equal to30%.
 10. The method as claimed in claim 9, wherein the rapid heattreatment process is performed with the ratio of the oxidizing gas inthe oxidizing atmosphere being more than or equal to 0.1% and less thanor equal to 30%.
 11. The method as claimed in claim 9, wherein the rapidheat treatment process is performed with the ratio of the oxidizing gasin the oxidizing atmosphere being more than or equal to 1% and less thanor equal to 20%.
 12. The method as claimed in claim 8, wherein saidcrystallizing the first conductive oxide film is performed at atemperature higher than or equal to 650° C. and lower than or equal to750° C.
 13. The method as claimed in claim 8, wherein said crystallizingthe surface of the second conductive oxide film is performed at atemperature higher than or equal to 650° C. and lower than or equal to750° C.
 14. The method as claimed in claim 8, wherein said depositingthe first conductive oxide film is performed by sputtering at atemperature higher than or equal to 150° C. and lower than or equal to350° C., so that the first conductive oxide film formed is in acrystalline state.
 15. The method as claimed in claim 8, wherein saiddepositing the first conductive oxide film is performed by sputtering ata temperature higher than or equal to 10° C. and lower than or equal to50° C., so that the first conductive oxide film formed is in anamorphous state.
 16. The method as claimed in claim 8, wherein saiddepositing the second conductive oxide film is performed by sputteringat a temperature higher than or equal to 50° C. and lower than or equalto 80° C., so that the second conductive oxide film formed is in anamorphous state.
 17. The method as claimed in claim 8, wherein each ofthe first and second conductive oxide films is an iridium oxide film.18. The method as claimed in claim 8, wherein said depositing the secondconductive oxide film is performed so that the second conductive oxidefilm is 100 nm to 150 nm in thickness.
 19. The method as claimed inclaim 8, wherein said depositing the first conductive oxide film isperformed so that the first conductive oxide film is 20 nm to 75 nm inthickness.
 20. The method as claimed in claim 8, wherein a ratio of aflow rate of an oxidizing gas to a flow rate of an inert gas is less insaid depositing the first conductive oxide film than in said depositingthe second conductive oxide film, so that the second conductive oxidefilm is higher in ratio of oxidation than the first conductive oxidefilm.